全文获取类型
收费全文 | 601848篇 |
免费 | 7197篇 |
国内免费 | 1972篇 |
专业分类
电工技术 | 11362篇 |
综合类 | 625篇 |
化学工业 | 88521篇 |
金属工艺 | 23878篇 |
机械仪表 | 19513篇 |
建筑科学 | 13379篇 |
矿业工程 | 2980篇 |
能源动力 | 16282篇 |
轻工业 | 45983篇 |
水利工程 | 6187篇 |
石油天然气 | 10602篇 |
武器工业 | 80篇 |
无线电 | 74611篇 |
一般工业技术 | 119500篇 |
冶金工业 | 112727篇 |
原子能技术 | 12854篇 |
自动化技术 | 51933篇 |
出版年
2021年 | 5301篇 |
2020年 | 4024篇 |
2019年 | 5142篇 |
2018年 | 8777篇 |
2017年 | 8855篇 |
2016年 | 9420篇 |
2015年 | 5992篇 |
2014年 | 9935篇 |
2013年 | 28414篇 |
2012年 | 15972篇 |
2011年 | 21699篇 |
2010年 | 17273篇 |
2009年 | 19502篇 |
2008年 | 20319篇 |
2007年 | 20072篇 |
2006年 | 18072篇 |
2005年 | 16209篇 |
2004年 | 15496篇 |
2003年 | 15408篇 |
2002年 | 14581篇 |
2001年 | 14444篇 |
2000年 | 13703篇 |
1999年 | 14284篇 |
1998年 | 35390篇 |
1997年 | 24673篇 |
1996年 | 19209篇 |
1995年 | 14504篇 |
1994年 | 12825篇 |
1993年 | 12807篇 |
1992年 | 9572篇 |
1991年 | 8992篇 |
1990年 | 8811篇 |
1989年 | 8299篇 |
1988年 | 7961篇 |
1987年 | 7020篇 |
1986年 | 6849篇 |
1985年 | 7771篇 |
1984年 | 7162篇 |
1983年 | 6438篇 |
1982年 | 5995篇 |
1981年 | 6159篇 |
1980年 | 5731篇 |
1979年 | 5545篇 |
1978年 | 5395篇 |
1977年 | 6250篇 |
1976年 | 7896篇 |
1975年 | 4794篇 |
1974年 | 4617篇 |
1973年 | 4673篇 |
1972年 | 3818篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
93.
94.
Malignant bone pain: pathophysiology and treatment 总被引:1,自引:0,他引:1
S Mercadante 《Canadian Metallurgical Quarterly》1997,69(1-2):1-18
2-acetyl aminofluorene (AAF) reacts in acidic conditions with nitrous fume yielding N-nitroso-AAF (N-NO-AAF), as previously described, that exerts more toxic and mutagenic effects than its parental compound. In this study, the effect of sodium nitrite (NaNO2) on the tumorigenicity of AAF in rats fed with AAF and NaNO2 was observed. Wistar rats were divided into five groups: group I served as control; group II were treated with NaNO2 (0.3%); group III was given 0.02% AAF alone; groups IV and V received both AAF and NaNO2 (0.2 and 0.3% respectively) in their diet for 12 weeks. At the end of the experiment, all rats in groups III, IV and V developed early stage phenomena of hepatocellular carcinoma, including hepatomegaly with variable-sized foci and neoplastic nodules. Severe damage was observed in the rats treated with AAF and NaNO2. Feeding of AAF (0.02%) for 3 months elevated the levels of c-Fos, c-Jun and c-Myc proteins in the rat livers. The AAF-induced c-Jun, c-Fos and c-Myc expressions were significantly magnified (P < 0.001) by NaNO2. These data confirmed that the strengthening of AAF-induced hepatocarcinogenesis by NaNO2 should be associated with its enhancing effect on the AAF-induced increases in the expressions of c-Jun, c-Fos and c-Myc. 相似文献
95.
96.
97.
I. S. W. B. Prasetya 《Formal Aspects of Computing》1994,6(4):466-470
UNITY, introduced by Chandy and Misra [ChM88], is a programming logic intended to reason about temporal properties of distributed programs. Despite the fact that UNITY does not have the full power of, for example, linear temporal logic, it enjoys popularity due to its simplicity.There was however a serious problem with the Substitution Rule. The logic is incomplete without the rule, and with the rule it is inconsistent. 相似文献
98.
Prolog/Rex represents a powerful amalgamation of the latest techniques for knowledge representation and processing, rich in semantic features that ease the difficult task of encoding heterogeneous knowledge of real-world applications. The Prolog/Rex concept mechanism lets a user represent domain entities in terms of their structural and behavioral properties, including multiple inheritance, arbitrary user-defined relations among entities, annotated values (demons), incomplete knowledge, etc. A flexible rule language helps the knowledge engineer capture human expertise and provide flexible control of the reasoning process. Additional Prolog/Rex strength that cannot be found in any other hybrid language made on top of Prolog is language level support for keeping many potentially contradictory solutions to a problem, allowing possible solutions and their implications to be automatically generated and completely explored before they are committed. The same mechanism is used to model time-states, which are useful in planning and scheduling applications of Prolog/Rex 相似文献
99.
Graefe G. Linville A. Shapiro L.D. 《Knowledge and Data Engineering, IEEE Transactions on》1994,6(6):934-944
Efficient algorithms for processing large volumes of data are very important both for relational and new object-oriented database systems. Many query-processing operations can be implemented using sort- or hash-based algorithms, e.g. intersections, joins, and duplicate elimination. In the early relational database systems, only sort-based algorithms were employed. In the last decade, hash-based algorithms have gained acceptance and popularity, and are often considered generally superior to sort-based algorithms such as merge-join. In this article, we compare the concepts behind sort- and hash-based query-processing algorithms and conclude that (1) many dualities exist between the two types of algorithms, (2) their costs differ mostly by percentages rather than by factors, (3) several special cases exist that favor one or the other choice, and (4) there is a strong reason why both hash- and sort-based algorithms should be available in a query-processing system. Our conclusions are supported by experiments performed using the Volcano query execution engine 相似文献
100.
Arguello F. Bruguera J.D. Doallo R. Zapata E.L. 《Parallel and Distributed Systems, IEEE Transactions on》1994,5(10):1091-1099
We present an unified parallel architecture for four of the most important fast orthogonal transforms with trigonometric kernel: Complex Valued Fourier (CFFT), Real Valued Fourier (RFFT), Hartley (FHT), and Cosine (FCT). Out of these, only the CFFT has a data flow coinciding with the one generated by the successive doubling method, which can be transformed on a constant geometry flow using perfect unshuffle or shuffle permutations. The other three require some type of hardware modification to guarantee the constant geometry of the successive doubling method. We have defined a generalized processing section (PS), based on a circular CORDIC rotator, for the four transforms. This PS section permits the evaluation of the CFFT and FCT transforms in n data recirculations and the RFFT and FHT transforms in n-1 data recirculations, with n being the number of stages of a transform of length N=rn. Also, the efficiency of the partitioned parallel architecture is optimum because there is no cycle loss in the systolic computation of all the butterflies for each of the four transforms 相似文献